So today we had a potential client call thinking that they need duct cleaning because their furnace is shutting off due to lack of airflow.

Now, we could’ve just said yes you need to get your ducts cleaned ASAP but that is not necessarily true and we asked a few questions from the client.

Our first question was how old is your furnace and is it a high efficient? If the answer was yes then it is possible that the secondary heat exchanger in the furnace which looks kind of like an air conditioning coil but is located right above the furnace blower is getting clogged up, but this was not the case, the client’s Furnace was amid efficient and does not have this secondary heat exchanger.

The next question that we asked was, do you have air conditioning? Now we asked this question because much like the first question an air conditioner will have a coil that sits above the furnace and can get clogged up with dust over time. This can lead to a lack of airflow that would cause the furnace to short cycle, or in the summertime could cause your air conditioner to freeze up and stop working until it thaws. Again though, this was not the case, the customer did not have air-conditioning.

This led me to ask the last question which is the most common reason for lack of airflow in a furnace system, and that is when is the last time you changed your filter? Usually, the answer comes back but they haven’t looked at it in a year or at least six months. This would lead me to believe that the filter is completely clogged up and needs to be replaced, and will most likely solve the problem of the furnace’s lack of airflow or high backpressure. Once again the customer surprised me with his answer saying that he just changed it last week, for a minute I figured that maybe the furnace fan was needing to be replaced, but then I asked him what the MERV rating was on the filter. When he told me that the MERV rating was at 12 I thought there could be one other culprit to the lack of airflow, and that is that the filter media is so dense that it is slowing down the airflow and creating enough back pressure to the point that it is triggering the furnace airflow sensor to go off.

I asked the client to pull the filter out and let the furnace run and see if this solves the problem, and it did. No, this doesn’t mean that the furnace doesn’t need to be serviced, or have a different filter put in, and perhaps the fan is getting weak and needs to be replaced or at least turned up to a higher speed if he wants to run with a filter that is that rating.

Remember, your furnace system can only handle so much back pressure before airflow sensors are going to start to go off, in the situation above it could’ve been any of the options I mentioned. I would suggest for typical residential systems a filter with a MERV rating of 11 is the maximum to go with if you’re picking up the filters from the hardware store.

If you’re interested in better indoor air quality you can contact us to do an indoor air quality test or get an estimate on a good filter, perhaps one that is 4 inches thick that you only have to replace annually as opposed to once every three months. For more information on filtration systems or if you’re looking for furnace and duct cleaning please give us a call.

In the end, I’m glad that we could help this client get their heat back on quickly without the expense of an after-hours furnace service call.